8/19/2019 9. Prestress Materials
1/24
REINFORCED CONCRETE ELEMENT II
INTRODUCTION TO PRESTRESSED CONCRETEPre-stressed Materials
M LUTFI MANFALUTHY
8/19/2019 9. Prestress Materials
2/24
OBJECTIVES2
Upon completion of this topic, student will be able to:
• Distinguish the differences between reinforcing steel and pre-stressing steel.
• Distinguish the shapes of pre-stressing tendons.
• Recognize mostly used stand types.
• Understand the effect of relaxation, temperature, fatigue, an corrosion
to pre-stressing steel.• Understand the composition of concrete used in pre-stressed
concrete.
• Recognize stress-strain diagram of concrete.
• Understand the most useful mechanical properties of concrete f!c,
f!tc, fr, "c, n#• Understand the effect of creep, $hrin%age, fatigue, temperature,
• and steam curing to pre-stressed concrete.
8/19/2019 9. Prestress Materials
3/24
8/19/2019 9. Prestress Materials
4/24
PRE-STRESSING MATERIALS4
aterial used in pre-stressed concrete are:
• &re-stressing steel• oncrete• uxiliary
nchorage *endon ducting
ement grout
8/19/2019 9. Prestress Materials
5/24
PRESTRESSING STEEL5
As prestressed looses in the steel (not inclde !riction" c#n o!ten
#ppro#ch $%%MP#& th#t is #'ot e#l to the t)pic#l )ieldstren*th o! o! co++on rein!orcin* '#rs& it is cle#r th#t +ini++tensile stren*th o! prestressed steel +st 'e hi*er th#n this,#le-
Ide#ll) # tendon +#teri#l shold not onl) h#,e hi*h stren*th 't
#lso.• re+#in el#stic pto rel#ti,el) hi*h stress
• sho/ s0cient dctilit) 'e!ore !#ilre
• h#,e *ood 'ondin* properties& lo/ rel#1#tion& *ood
resist#nce to• !#ti*e #nd corrosion
• 'e econo+ic#l #nd e#s) to h#ndle
8/19/2019 9. Prestress Materials
6/24
Type of pre-!re"#$ !e#%o#&'
Cortes) o! S+ito+o2s Tensionin* M#teri#ls& 3#p#n
8/19/2019 9. Prestress Materials
7/24
Type of pre-!re"#$ !e#%o#&(
8/19/2019 9. Prestress Materials
8/24
Me)*+#")+, +#% S!re-S!r+"# proper!"e
Mini++ Properties o! pre4stressin* tendon-
8/19/2019 9. Prestress Materials
9/24
S!re-!r+"# %"+$r+. of pre-!ree"#$ !ee,/
Fro+ 5*re& prestressin*steel.• O6er s'st#nti#ll) hi*her
stren*th th#n rein!orcin*steel #cco+p#nied ')
lo/er !#ilre str#in-• Do not sho/ /ell de5ned
)ieldin* 'eh#,ior-• H#,e rel#ti,el) hi*h
proportion#l li+its-
8/19/2019 9. Prestress Materials
10/24
S!ee, Re,+0+!"o#1
Relaxation is the loss of tension o)er time in a stressed tendon maintained at
constant length and temperature. *he relaxation is negligible for stress smaller
than /0 percent of ultimate strength. *emperature increase also caused significant
effect on loss of stress in prestressing steel.(*$ $urabaya# Reinforced oncrete ((
8/19/2019 9. Prestress Materials
11/24
8/19/2019 9. Prestress Materials
12/24
S N Cre +#% S."!* D"+$r+.12
8/19/2019 9. Prestress Materials
13/24
CORROSION13
*he magnitude and conse'uences of corrosion in prestressing
steel are mush more se)ere than in reinforcing steel. *his is notonly high-grade steel is more susceptible to corrosion but also
because the diameter of prestressing tendon is relati)ely small.
*hus e)en small corroded spot substantially reduce the cross-
sectional area of steel.
&restessing steel are generally susceptible to two ma6or types of corrosion:• "lectro chemical corrosion.
an a'ueous solution must be present, e)en in the form of thin
film, and air oxygen# is needed.
• $tress corrosioncauses brittleness in the steel under certain conditions of stress
and en)ironment.
*o guard against corrosion, prestressing steel must be transported
and stored in closed waterproof container.
8/19/2019 9. Prestress Materials
14/24
CONCRETE14
oncrete is a )ersatile composite material of a )ery complex nature, yet
it can be approached at any desired le)el of sophistication.
*he technical le)el at which concrete must be approach is higher in
prestressed concrete than in reinforced concrete. (n designing
prestressed concrete, the designer does not only consider the strength
of concrete but also its time-dependent properties such as creep and
shrin%age.
8/19/2019 9. Prestress Materials
15/24
CONCRETE STRESS STRAIN CURVE15
• 7eft figure shows stress strain diagram
of concrete, first part is ascending
portion up to the pea% point maximum
stress# and descending portion, the
strength, f8c , corresponds to the
maximum stress.
• (t can be obser)ed that the higher the
concrete strength, the steeper the
descending portion of the stress-strain
cur)e. steep descending portion is
often associated with brittleness or lac%of ductility of material.
8/19/2019 9. Prestress Materials
16/24
De!er."#+!"o# of Mo%, fro. S!re-S!r+"# D"+$r+.1'
Fro+ stress4str#in di#*r#+ SNI7ACI se el#sticit) (Ec" ,#le t#8en thet#n*ent o! line !ro+ ori*in to point %-$9!2c(ITS Sr#'#)#" Rein!orced Concrete II
8/19/2019 9. Prestress Materials
17/24
ELASTICIT6 FROM SEVERAL CODES1(
8/19/2019 9. Prestress Materials
18/24
CONCRETE S7RIN8AGE1
• Concrete cont#ined +ore/#ter th#n is strictl)reired ') che+ic#lre#ction o! ce+ent- Thee1cess /#ter c#lled !ree/#ter& its loss thro*h
e,#por#tion le#ds to*r#d#l shortenin* o!+e+'er /ith ti+e&descri'ed #s shrinkage-
• As the +e+'er shortens&
the prestressin* steel losesp#rt o! its prestress& this isc#lled shrinkage loss-
8/19/2019 9. Prestress Materials
19/24
CONCRETE CREEP1/
• Creep is ti+e dependent str#in ine1cess o! el#stic str#in indced in+#teri#l s':ected to # sst#inedstress-
• Unli8e shrin8#*e& creep is c#sed
') lo#din*- I! the lo#d is re+o,ed&the initi#l el#stic str#in is reco,eredi++edi#tel)- A p#rt o! the creepstr#in is *r#d#ll) reco,ered o,erti+e #nd re+#inin* p#rt is non4reco,er#'le-
• E6ect o! #*e #t lo#din* isrepresented on le!t 5*re- One tonoted th#t e#rlier the prestressin*lo#d& hi*her the loss o!prestressin*-
8/19/2019 9. Prestress Materials
20/24
DISPLACEMENT CAUSED B6 CREEP2
• As pointed ot e#rlier& thecreep o! concrete le#ds notonl) losses o! stress in theprestressin* steel& 't #lsoto lon* ter+ de!or+#tion orde;ection o! the strctre-
This illstr#ted in le!t 5*re-• Note th#t the de;ection
cr,e !or const#nt lo#d is,er) si+il#r in sh#pe to thecr,e o! creep str#in nderconst#nt lo#d-
• For #ct#l condition in the5eld /here continos,#ri#tion in te+per#tre #ndh+idit)& /ill le#d to;ct#tin* cr,es /ith +ch
less de5ned li+itin* ,#les-
8/19/2019 9. Prestress Materials
21/24
CONCRETE FATIGUE21
It is *ener#ll) o'ser,ed th#t concrete in direct co+pression c#n
sst#in # ;ct#tin* stress 'et/een o to 9% percent o! its st#ticco+pressi,e stren*th !or #t le#st
8/19/2019 9. Prestress Materials
22/24
EFFECT OF TEMPERATURE ON CONCRETE22
Concrete he#ted p to =%%C does not nder*o si*ni5c#ntph)sic#l or che+ic#l ch#n*es- It *ener#ll) loses its !ree /#ter#t
8/19/2019 9. Prestress Materials
23/24
REMAR8S23
• The +#teri#l properties s++#ri@ed here #re essenti#lele+ents to the !ll nderst#ndin* o! restressed concrete'eh#,ior- The) help to cl#ri!) the '#sic !or +#n) desi*nprocedres tre#ted l#ter-
• Not #ll the properties #re o! i++edi#te se in desi*n-Ho/e,er& the +ore 5n#l the desi*n& #nd the +ore co+ple1
the strctre& the *re#ter is the need to #ccont in desi*n !orthe #ct#l 'eh#,ior o! the +#teri#ls #nd their inter#ction-
• Prestress losses depend not onl) on +#teri#l properties 't#lso on strctr#l 'eh#,ior #nd en,iron+ent#l condition- Atthis point& their i++edi#te #nd thoro*h tre#t+ent +#)
con!se /ho ne/l) #c#inted /ith prestressed concrete-
8/19/2019 9. Prestress Materials
24/24
Re"#for)e% Co#)re!e E,e.e#! II
THAN YOU
Top Related